The present invention relates to a process for producing a silver halide photographic paper incorporating a silver halide developing agent. More particularly, the present invention relates to a process for producing a photographic paper that has improved photographic performance in such aspects as speed and contrast, as well as high pressure resistance, good developability and long keeping quality and which ensures a high degree of whiteness even if it is processed under rapid conditions.
Techniques for achieving good developability have hitherto been proposed such as use of a halide converted emulsion as described in Japanese patent application (OPI) No. 3339/1971 (the term OPI as used hereinafter means an unexamined published Japanese patent application). However, under very rapid processing conditions such as to complete the development within 30 seconds, good developability cannot be achieved to a full extent.
With a view to achieving good developability under very rapid processing conditions, it has been practiced widely to incorporate, in light-sensitive materials, black-and-white developing agents such as hydroquinones, Metol and Phenidone, or color developing agents such as p-phenylenediamine derivatives.
The use of fluorescent brighteners is a well known technique for increasing the whiteness of silver halide photographic paper after processing. For attaining this purpose, oil-soluble brighteners are superior to water-soluble brighteners since they will not be easily lost from the light-sensitive material during processing. Techniques for incorporating oil-soluble brighteners in light-sensitive materials are described in BP No. 1,072,915, Japanese patent publication No. 37376/1970 and Japanese patent application (OPI) No. 134232/1985 (the term OPI as used hereinafter means an unexamined published Japanese patent application), etc. Basically, the methods disclosed in these patents consist of first dissolving oil-soluble brighteners in organic solvents, then forming emulsified dispersions from the solutions, and incorporating them in light-sensitive materials. Japanese patent application (OPI) No. 134232/1985 specifically mentions reduced brightening effects as a problem that is caused by the coexistence of an oil-soluble brightener and a developing agent in the same light-sensitive material, and it proposes a method for solving this problem. Another problem that occurs when both an oil-soluble brightener and a developing agent are present in the same light-sensitive material is that the intensity of fluorescence decreases as the light-sensitive material is stored for a prolonged time. This time-dependent deterioration of fluorescence intensity is of such a great degree as has never been observed with light-sensitive materials that do not contain incorporated developing agents.
In recent years, the demand for improving the photographic performance of light-sensitive materials in such aspects as speed and contrast is constantly increasing. However, the improvement in speed is not preferable from the viewpoint of pressure resistance, particularly in the case of silver halide photographic materials using a high-sensitive silver iodobromide emulsion.
As pressures (mechanical stress) to photographic materials, friction to be caused by feeding frames at the time of taking pictures as in the case of conventional photographic films, folding which occures in large-sized photographic sheets at the time of handling as in the case of printing and X-ray photographic materials, and the like are called in question. Among the problems arising from the above-mentioned pressures, "pressure marks" are particularly problematical as the quality of images obtained from the photographic materials is strikingly damaged.
One method of improving the pressure resistance is disclosed in Japanese patent application (OPI) No. 147727/1985, in which a multi-layer type emulsion containing grains having some layers which are different in iodo content or grains having inner layers of high iodo content is used. However, the effect in respect of pressure resistance is not sufficient.
Another method of improving the pressure resistance is disclosed in Japanese patent applications (OPI) Nos. 122641/1985, 3339/1971 etc., in which good pressure resistance is obtained by using an emulsion prepared by halide conversion. However, the photographic materials produced by this method tend to cause the lowering of contrast particularly at the high density side, and, therefore, is not satisfactory at all in photographic performance.
Still another method of improving the pressure resistance is disclosed in Japanese patent applications (OPI) Nos. 51733/1981, 147142/1981, etc., in which irridium salts are contained in the silver halide grains to improve the pressure resitance. However, the photographic materials produced by this method are insufficient in pressure resistance and, also, inferior in keeping quality.
Still another method of improving the pressure resistance is disclosed in Japanese patent publications Nos. 5017/1974, 28086/1978, etc., in which, as means to improve the pressure resistance from the point of physical properties, a plasticizer such as polymer is added to the silver halide emulsion layer to relax the pressure. However, this method is not effective for all the mechanical stresses in that the plasticizer per se causes deterioration in film strength and, therefore, is limited in the amount to be used and that the photographic materials produced by the method become worse in pressure marks such as abrasion caused by friction with a very hard thing.